The invention relates to a pressure transducer. In particular the invention relates to a pressure transducer arranged in a casing and having a measuring diaphragm.
Such pressure transducers are known, for example from the European patent No. 0 033 749. There, a pressure gauge head is disclosed, which contains a measuring diaphragm of silicon in a cylindrical casing. The excursion of the diaphragm serves as a measure of a pressure difference acting on the front faces of the diaphragm. The diaphragm divides the interior space of the casing into two gas-tight chambers sealed against each other. The chambers are in each instance provided with inlet tubes, which guide the pressure to be measured from the measuring site into the chambers. The excursion of the diaphragm is measured by way of a resistance change in piezoresistive resistance elements which are diffused into the silicon diaphragm. The electrical signal corresponding to the resistance change is led out of the casing of the pressure gauge head through gas-tight electrical lead-throughs.
Conversion of the diaphragm excursion into an electrical signal takes place, for example, with a capacitive measuring arrangement (EP-A2-0 195 985) or a ring oscillator circuit (EP-A2-0 040 795) integrated into a silicon diaphragm.
In modern measuring and automation technology the demand has risen for sensors and signal processing systems connected to the sensors. The signal processing systems are in a position to detect faulty functioning of the sensor and to reduce the effect of such faulty functioning to a large extent. Such faulty functioning can be caused by the sensor itself, for example, through a change of its sensitivity and its zero point. An important source of errors can, however, also be coupling of the sensor to the physical variable. Monitoring the entire measuring chain, which includes the sensor and the succeeding signal processing systems, is more advantageous the closer to the start of the measuring chain the monitoring intervenes.
However, with the known pressure transducers, self-monitoring is not possible. Faulty functioning of these pressure transducers can only be recognized when the transducer is uncoupled from the physical variable to be measured and subjected to a separate calibration. While this calibration is in progress, the sensor is not available for the actual measuring process.